That sounds like an interesting thing to do, especially as many plants are known to take up large quantities of nitrogen from the soil, and high levels of nitrates and nitrites in plants are not good for tortoises (which is why we suggest growing weeds on unfertilised soil). Unfortunately I've never done any testing myself so I don't know which test kits would be best. If you google 'kits for testing nitrogen content in soil' or a similar phrase lots of results come up, including several YouTube videos demonstrating how to do it.

Hopefully someone who is better at testing soil will come on with a suggestion of some good products.

Hi again,
I've just had an email from Jon, one of my TTT colleagues, who know much more about this than I do. He says that he thinksif you want a really accurate answer you need to use a lab. Here is what he wrote when I told him someone was asking about testing for nitrogen in their soil:

It would need to be sent to a lab, however most labs do not test nitrogen as standard because nitrates are converted into the diatomic nitrogen gas in short periods of time. He/she would need to request the test and I think it requires freezing and delivery this way (expensive I guess).
My understanding is that the home kits are very poor because the water (which is the solvent) affects the nitrogen forms/availability and there is no way to know how nitrogen has actually gone into solution (soil humus/clay acts a ‘colloid’). If they are concerned, it might be worth planting species that require nitrogen rich soil, however nitrogen does escape into gas by bacteria on its own accord (much better explained here https://en.wikipedia.org/wiki/Denitrification).

So that is what Jon said. I did read also that testing for nitrogen needs to be done at specific times of the year, as levels of nitrogen in the soil can vary considerably at different times of the year (for example in autumn various vegetable matter is breaking down). One place said the Spring is considered the best time for testing (but I can't remember why!).

I don't know if this has been of any help, and it occurs to me that I don't know why you are testing for nitrogen content. The reason I ask is that there might be another solution to your reason for wanting to know about the nitrogen content, depending on what your question is.

Hi Nina, Thank you very much for the info on testing for nitrogen and please pass on my thanks to the gentleman who helped explain. The reason I'm asking is because I'm still in the process of making sure my tortoise garden is safe for a potential rehoming. It is definitely in a much better state than last year and I have managed to grow some musk mallow which in your plant database specifys that if there is nitrogen in the soil it can get into the mallow leaves which isn't good for tortoises and I just wanted to make sure the mallow was safe. As far as I know the soil doesn't have anything dug into it. But when we had our garden renovated 2 years ago the gardeners did add some extra earth to the area. One thing tho it was very good at growing dandelions this year! Which I have removed a good quantity of, just leaving a few, as I read too many dandelions aren't good either and I wanted more room to grow other tortoise friendly weeds and plants. With the nitrogen question I was really just wanting to make sure the musk mallow will be safe.

Thanks for expaining, and I think your soil will be just fine to grow things for your tortoise. The mallows will take up nitrogen, but almost all soil will have nitrogen in it, as plants need it for healthy growing, but it's just that some plants take up more nitrogen than others. The only thing to worry about is if lots of fertiliser has been added to the soil, thus increasing the amount of nitrogen taken up by the plants, and that hasn't happened with your garden. The extra earth that the gardeners dug into the area was probably just topsoil, or a decent compost, but even if it was heavily enriched earth, the extra nitrogen in that will have been used up a long time ago, so I think you will be just fine.

It's great that you will be growing tortoise-friendly plants, so good luck and let us know how you get on.